In recent years, complementary metal-oxide semiconductor (CMOS) image sensors, which feature low cost since they are mass-producible in a simple manufacturing process, small power consumption since the element sizes are small, and so on, compared with charge-coupled device (CCD) image sensors, have attracted attention.
In CMOS image sensors, a rolling shutter system in which the shutter is sequentially released for each scan line is typically employed to read captured-image signals. When the rolling shutter system is employed to read captured-image signals of all pixels in one frame, signals are read line by line in sequence from the uppermost line in a pixel array toward the lowermost line in the pixel array. Thus, a time difference occurs between when the reading is started and when the reading is completed, so that the exposure timing at an upper portion of a screen and the exposure timing at a lower portion thereof differ from each other. Consequently, when a camera having a CMOS image sensor is used to capture an image of a moving subject, a rolling shutter phenomenon, in which the subject is obliquely distorted in the captured image, occurs. The rolling shutter phenomenon may also be called the focal plane phenomenon.
There are also related technologies in which two images acquired sequentially are combined to correct an image in which the rolling shutter phenomenon occurs. In the related technologies, the scan direction for a first image and the scan direction for a second image are set to be different from each other to thereby cause the directions in which distortions occur to differ from each other. The first and second images in which the directions of the respective distortions differ from each other are combined to correct moving-subject distortion in the captured image. These technologies are disclosed in, for example, Japanese Laid-open Patent Publication No. 2011-004068, Japanese Laid-open Patent Publication No. 2010-154390, Japanese Laid-open Patent Publication No. 2006-148861, and Japanese Laid-open Patent Publication No. 2006-033381.